Behind the scenes: Court speeds

Balls and rackets may be the buzz words when it comes to tennis equipment but it is the courts that often have the biggest influence on a match. Whether clay, grass or hard, it is the court to which players must adapt their game.

The court influences how the balls bounce and how a player moves, so it is little surprise they are put through just as rigorous tests by the International Tennis Federation as the rackets and the balls.

“The technical department has a mission statement and in summary we have a mission to protect the nature of the game,” says ITF Sports Engineer James Spurr. “That involves protecting the traditions that are very much associated with the sport of tennis but also we encourage innovation and technology.”

To ensure they are evolving with the technology, the ITF’s technical commission meets twice a year and presents research and data analysis.

“We have representatives from the tennis tours, a couple of university professors who are involved in sports engineering, members from court building associations as well as ITF,” says Spurr. “What we have at the ITF is the power to change the rules of tennis if we want to.”

The ITF outline four key properties for a court surface: friction, energy restitution (the energy returned by the surface and ball following impact), topography and dimensions, and consistency.

Courts are tested both on-site and at the ITF’s research facility in Roehampton using a series of trials. Following installation, on-site courts have to be stabilised before they can be tested, which can take several months.

Testing then commences with a visual inspection, ensuring all markings are straight and there are no cracks in the surface. A high specification ball is used to determine Court Pace Rating (CPR), with tests carried out in at least four different areas, such as high (around the baseline) and low (closer to the net) usage areas and on court markings.

To determine the pace of a court, balls are fired from an air-powered cannon on to the test surface area through two boxes at a speed of 30 m/s and at an approach angle of 16 degrees. Lasers in the boxes then reconstruct the trajectory of the ball before and after impact to determine the pace.

The CPR used to be Surface Pace Rating but was updated in 2008 to include the coefficient of restitution (how the ball bounces when dropped) and speeds are now classified in one of five categories: slow, medium-slow, medium, medium-fast or fast.

“We did a study where we took players’ perceptions of courts we measured and found that by including restitution the correlation between player perception and our measurement improved quite dramatically so we then changed Surface Pace to Court Pace classification,” explains Spurr.

The tests also look at the evenness of the surface, slope and dimensions, while maximum and minimum air temperature, humidity and atmospheric pressure are all recorded and balls are not subjected to more than 12 impacts each to ensure their original properties are not altered.

Results are then submitted into a report and compared against the average in the category or recommendation. Information and videos from field tests helps the ITF to better design the tests they do in the laboratories, as Spurr explains.

“We do a lot in the lab but we also do a lot out in the field, various projects take high-speed video cameras out and just film. High-speed cameras look for spin rates, software that can track ball and measure spin, track how far players move, speed, step lengths and the type of movement,” he said.

“The idea is to ecologically validate the equipment so that the data we produce is relevant to the game of tennis. There are a million ways of testing a racket or a ball but the majority of those would be completely pointless because they won’t actually tell you anything about the sport.”

Nine different generic court surfaces are tested by the ITF, including acrylic, artificial grass, carpet and clay. Surface products, of which there are over 250, are then given a code depending on which generic category they fall into and are also divided into the five CPR categories. CPR classification is valid for three years, after which time products will be retested.

While the classification does not imply ITF approval or endorsement, court owners can apply for ITF Recognition, an acknowledgement that the court meets the recommendations provided in the ITF’s test methods.

Recognition is targeted at venues hosting elite-level competition and there are two levels: One-Star ITF Recognition (court is tested for quality of installation) and Two-Star ITF Recognition (court is also tested for pace). For the Davis Cup and Fed Cup there are regulations for venues with acrylic courts that they must fall within the 24-50 CPR bracket.

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